1. Field of the Invention
The present invention relates to aircraft wheels of the type having a rim for supporting a pneumatic tire, and more particularly to an improved fatigue reducing rim configuration and technique.
2. Description of the Related Art
In one form, a typical wheel rim for aircraft may include a rim body having an integral inboardly positioned tire bead flange, a demountable separable outboardly positioned tire bead flange, a split lock ring seated within an annular groove in the rim body and, perhaps, an arrangement associated with the lock ring to maintain it on the wheel rim independent of tire inflation. In wheel rim assemblies of this type, a deflated tire is firstly mounted on the rim body and it is followed by the demountable bead flange which is moved inboardly on the rim body such that the split lock ring may be seated within the annular groove provided for it proximate the outboard edge of the rim body. Upon inflation of a mounted tire, the demountable bead flange is moved outboardly on the rim and into forceful engagement with the split lock ring. Frequently, the lock ring or retaining ring and separable bead flange have mating conical tapers and the outward motion of the separable bead flange urges, by way of the engaged conical tapers, the retaining ring radially inwardly into the retaining ring annular groove. These conical tapers are flat, that is, they are surfaces of revolution of a straight line. Alternatively, when the tire is to be demounted from the rim, it is firstly deflated and the demountable bead flange is moved inboardly to disengage the lock ring. The split lock ring may then be removed from within its mounting groove and the demountable bead flange and deflated tire removed from the rim body in the outboardly direction. Demountable flange aircraft wheel designs are currently used for applications such as military aircraft wheels. These designs are low mileage wheels. It is desirable to provide demountable flange wheels for nonmilitary wheel applications. Military demountable flange wheels can exhibit fatigue problems if used for longer life nonmilitary applications. Load is transmitted, for example, from the tire by way of the separable bead flange and retaining ring to the groove in the wheel rim. Frequently, stress problems appear near the base of the wheel rim groove or in the removable flange where it contacts the retaining ring. Such tensile stresses in the groove in the rim body can cause fracturing and an early retirement of the wheel rim. Additional material in the high stress regions can eliminate the problem, but only at the expense of added weight detracting from the aircraft payload. The present invention improves the demountable flange and retaining ring geometries without increasing wheel weight to minimize fatigue damage and enables the use of demountable flange wheels for nonmilitary wheel applications.
The present invention provides an optimization of the geometry for demountable flange wheels. This invention incorporates curved contact surfaces for the interface between the demountable flange and retaining ring to direct the flange loads more efficiently into the wheel. This invention also uses a compound radius between the retaining ring and wheel to distribute the directed load as a uniform contact stress. The result is the elimination of fatigue (crack initiation) in the retaining ring radius and the minimization of fretting fatigue between the demountable flange and retaining ring, and between the retaining ring and wheel.
The invention comprises, in one form thereof, a tire receiving wheel rim assembly having an annular wheel rim with a first bead flange, a second separable bead flange, and a retaining ring which may be placed within a groove in the wheel rim engaging both the wheel rim and a region of the separable bead flange to secure the separable bead flange to the wheel rim and retain an inflated tire between the bead flanges. The region of engagement between the separable bead flange and retaining ring has abutting annular surfaces, each of which, in cross-section, has a finite radius of curvature. The abutting portion of the retaining ring annular surface may be convex and the abutting portion of the separable bead flange surface concave. Both radii of curvature are constants and the radius of curvature of the separable bead flange surface exceeds the radius of curvature of the retaining ring surface. The region of engagement between the separable bead flange and retaining ring is limited to the abutting annular surfaces and the separable bead flange and retaining ring are otherwise spaced apart from one another.
An advantage of the present invention is that the magnitude of stresses is reduced significantly increasing wheel life without increasing wheel weight.